Field
This disclosure relates generally to mole or gas delivery devices, and more particularly, to a method of and system for pulse gas delivery. As used herein the term “gas” includes the term “vapor(s)” should the two terms be considered different.
Overview
The manufacture or fabrication of semiconductor devices often requires the careful synchronization and precisely measured delivery of as many as a dozen gases to a process tool. For purposes herein, the term “process tool” may or may not include a process chamber. Various recipes are used in the manufacturing process, involving many discrete process steps, where a semiconductor device is typically cleaned, polished, oxidized, masked, etched, doped, metalized, etc. The steps used, their particular sequence, and the materials involved all contribute to the making of particular devices.
As device sizes have shrunk below 90 nm, one technique known as atomic layer deposition, or ALD, continues to be required for a variety of applications, such as the deposition of barriers for copper interconnects, the creation of tungsten nucleation layers, and the production of highly conducting dielectrics. In the ALD process, two or more precursor gases are delivered in pulses and flow over a wafer surface in a process tool maintained under vacuum. The two or more precursor gases flow in an alternating or sequential manner so that the gases can react with the sites or functional groups on the wafer surface. When all of the available sites are saturated from one of the precursor gases (e.g., gas A), the reaction stops and a purge gas is used to purge the excess precursor molecules from the process tool. The process is repeated, as the next precursor gas (i.e., gas B) flows over the wafer surface. For a process involving two precursor gases, a cycle can be defined as one pulse of precursor A, purge, one pulse of precursor B, and purge. A cycle can include the pulses of additional precursor gases, as well as repeats of a precursor gas, with the use of a purge gas in between successive pulses of precursor gases. This sequence is repeated until a final geometric characteristic, such as thickness, is reached. These sequential, self-limiting surface reactions result in one monolayer of deposited film per cycle.
The delivery of pulses of precursor gases introduced into a process tool can be controlled using a pulse gas delivery (PGD) device. PGD devices control the flow of gas into and out of a delivery chamber of a known volume by controlling the opening and closing of inlet and outlet on/off-type valves in order to control the flow of gas into and out of the chamber, and using the timing of the opening of the outlet shutoff valve to deliver a desired amount (mass) of precursor gas as a pulse into the process chamber of the process tool. Alternatively, a mass flow controller (“MFC”), which is a self-contained device comprising a flow meter, control valve, and control and signal-processing electronics, has been used to deliver an amount of gas at predetermined and repeatable flow rates, in short time intervals.
More recently, certain processes have been developed that require high speed pulsed or time-multiplexed processing. For example, the semiconductor industry is developing advanced, 3-D integrated circuits thru-silicon vias (TSVs) to provide interconnect capability for die-to-die and wafer-to-wafer stacking. Manufacturers are currently considering a wide variety of 3-D integration schemes that present an equally broad range of TSV etch requirements. Plasma etch technology such as the Bosch process, which has been used extensively for deep silicon etching in memory devices and MEMS production, is well suited for TSV creation. The Bosch process, also known as a high speed pulsed or time-multiplexed etching, alternates repeatedly between two modes to achieve nearly vertical structures using SF6 and the deposition of a chemically inert passivation layer using C4F8. Targets for TSV required for commercial success are adequate functionality, low cost, and proven reliability.
These high speed processes require fast response times during the transition time of the pulses in order to better control the processes, making the use of pressure based pulse gas delivery devices problematic. Currently, one approach to increase response time is to use a fast response mass flow controller (MFC) to turn on and off gas flows of the delivery pulse gases delivered to the process tool according to signals received from a host controller. The repeatability and accuracy of pulse delivery using a fast response MFC with a host controller, however, leaves room for improvement, because response times are dependent on the workload of the host controller. The host controller may be prevented from sending timely control signals if it is performing other functions that require its attention. Further, with short duration control signals being sent from the host controller to the mass flow controller, communication jitter can occur causing errors in the delivery of pulses of gas. Workload of the host controller and communication jitter are two sources of error that reduce the repeatability and accuracy of pulse gas delivery when relying on fast communication between the host controller and the mass flow controller delivering pulses of gas.
In some instances it is desirable to provide multiple gases to a process tool. Accordingly, multiple channel versions of PGD devices have been developed. The exemplary PGD device 40 of FIGS. 1 and 2 includes a host controller 42 for controlling the flow through multiple channels using an MFC 44. Each MFC 44 is a self-contained device comprising a flow meter, control valve, and control and signal-processing electronics. In general the host controller controls the flow of gas through the MFC by controlling the setpoint to the MFC. The MFC then controls the position of the control valve as a function of the set point of the flow rate provided by the host controller/user and the actual flow rate measured by the flow meter. In the device shown in FIG. 2, a three-way isolation valve 46 is also provided for each channel for controlling the flow either to the process tool (chamber) when needed for an ongoing process, or diverting the gas through dump line 48 when gas is not needed for the process. The configuration shown in FIG. 1 has speed, accuracy, repeatability and reliability issues, while the configuration shown in FIG. 2 has accuracy, repeatability and reliability issues and waste gas through the dump lines.
FIG. 3 shows another multichannel PGD device arrangement 50. Each channel is provided with a delivery chamber 56 of a predetermined volume. Inlet and outlet ON-OFF (shut-off) valves 62 and 64 are provided at the inlet and outlet of each delivery chamber 56. The pressure and temperature of the gas in each chamber is sensed by a corresponding pressure and temperature sensor 58 and 60. The outputs of the pressure and the temperature sensors are provided to the dedicated controller 52, which in turn receives instructions from the host controller or user interface 50 over bus 54. A pulse of gas is delivered through a channel by closing the outlet valve 64 and opening the inlet valve 62 of the channel so as to allow the pressure to build up in the corresponding delivery chamber 56 to a certain determinable level, closing the inlet valve and opening the output valve allow gas to flow out of the outlet valve for a predetermined amount of time so as to deliver a measurable amount of gas (“Δn”) as a function of the volume of the delivery chamber (V), the temperature of the gas (T) as measured by the temperature sensor 60, the pressure (P) in the chamber as measured by the sensor 58, and the rate of decay of the pressure as the gas flows out of the chamber all in accordance with the ideal gas law,
                              Δ          ⁢                                          ⁢          n                =                              V            R                    ⁢          Δ          ⁢                                          ⁢                      (                          P              T                        )                                              (        1        )            where R is the universal gas constant.
Once the pulse is delivered the outlet valve of the channel can be closed. The delivery chamber can then be charged with gas by opening the inlet valve until the chamber charged to the desired pressure level, and the operation repeated for the delivery of the next pulse of gas. This arrangement, however, cannot deliver constant flows where they might be required. In addition, the rate at which one can deliver pulses of gas is constrained by the time it takes to charge and discharge the delivery chamber. Finally, relative to the other arrangements, the cost of this arrangement can be an issue, depending on the user's requirements.
Description of Related Art
Examples of pulse mass flow delivery systems can be found in U.S. Pat. Nos. 7,615,120; 7,615,120; 7,628,860; 7,628,861, 7,662,233; 7,735,452 and 7,794,544; U.S. Patent Publication Nos. 2006/0060139; and 2006/0130755, and pending U.S. application Ser. No. 12/689,961, entitled CONTROL FOR AND METHOD OF PULSED GAS DELIVERY, filed Jan. 19, 2010 in the name of Paul Meneghini and assigned the present assignee; and U.S. patent application Ser. No. 12/893,554, entitled SYSTEM FOR AND METHOD OF FAST PULSE GAS DELIVERY, filed Sep. 29, 2010 in the name of Junhua Ding, and assigned to the present assignee; and U.S. patent application Ser. No. 13/035,534, entitled METHOD AND APPARATUS FOR MULTIPLE-CHANNEL PULSE GAS DELIVERY SYSTEM, filed Feb. 25, 2011 in the name of Junhua Ding and assigned to the present assignee.